Notochord

The notochord is a flexible, rod-shaped body found in embryos of all chordates. It forms the axis of the embryo. In some chordates, it persists throughout life as the main support down the length of the body. In most vertebrates it is replaced by the vertebral column. The notochord is found ventral (underneath) the neural tube (future spinal cord).

Notochords were the first "backbones" in chordates. Notochords were advantageous to primitive fish-ancestors: they were a rigid structure for muscle attachment, but flexible enough to allow movement. Embryos of vertebrates have notochords, and develop the vertebral column later.

Notochord Media

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  Surface view of embryo of Concolor gibbon (Hylobates concolor).

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  Diagram of a transverse section, showing the mode of formation of the amnion in the chick.

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  Section through the head of a human embryo, about twelve days old, in the region of the hind-brain.

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  Transverse section of human embryo eight and a half to nine weeks old.